Hi, welcome to the site, depending which handbook you've been recommended these two threads may help: EYE level 3
www.silkysteps.com/forum/showthread.php?t=61978
and CYPW level 3 cognitive/intellectual development
https://www.silkysteps.com/forum/showthread.php?p=63228
and
pages 23 of this EYE handbook looks at how it's thought the brain develops after birth / post natal and the pattern of neurological, brain development along with theories about current research - how it's thought the majority of brain cells are formed before birth, but that most of the connections amongst the cells are made during infancy and early childhood. Referred to as plasticity of the brain it's believed that early experiences are vital to healthy brain development as the outside world shapes the development of their brain through experiences that a child senses - vision, hearing, smell, touch and taste.
Page 24 & 25 then look into each aspect of sensory development during the first year - search for 'sensory development' inside the
amazon preview.
Hope this helps a little